Hydratable (or hydraulic) cements, such as Portland cement, are useful in forming structural formations, such as building members, precast members and the like. These hydratable cements are mixed with aggregate to form mortars (cement, small aggregate, such as sand, and water) or concrete (cement, small aggregate, large aggregate, such as stone, and water) and structures made therefrom. It is highly desired to increase the flow (slump) properties of the initially formed hydratable cement composition to aid in placement of the composition and to extend the period of high flowability in order to provide working time to finish the placement of the structure. While extending the period of time that high slump is imparted to a cement composition, it is not desired to have the initial set time significantly delayed as such delay would disrupt the desired work schedule and delay completion of the structural formation.
Increased flowability can be attained by using large dosages of water in the hydrating cement composition. However, it is well known that the resultant cement based structure will have poor compressive strength and related properties which will make it unsuitable as a structural formation. Various additives have been proposed to increase the flowability to hydraulic cement compositions without increasing the water content of the initially formed composition. Such additives have been classified as “water reducing” admixtures or “superplasticizers,” and these include, for example, compounds such as naphthalene or melamine sulfonate formaldehyde condensates, lignin sulfonates and the like. In certain instances, the “water reducers” or “superplasticizers” have been used as a means of reducing the water to cement ratio in the composition (to enhance the strength of the resultant structure) without comprising flow properties.
More recently, copolymers of alkenyl ethers and acrylic acid or maleic anhydride, and derivatives thereof, have been proposed as agents suitable to enhance slump. See. e.g., Japanese Patent Publication (Kokai) Nos. 285140/88 and 163108/90. Further, copolymers formed from the copolymerization of hydroxy-terminated allyether and maleic anhydride or the allyether and a salt, ester or amide derivative of maleic anhydride such as disclosed in U.S. Pat. No. 4,471,100 have been proposed as cement admixtures capable of enhancing slump. Still further, U.S. Pat. No. 5,369,198 teaches the use of maleic acid derivatized polymers as a suitable water reducer.
In each of the above instances, the proposed cement admixture agents when used in a cement composition do not provide the desired combination of properties or only provide them in low degrees. For example, esterified acrylate copolymers, while providing good slump enhancement, also causes the treated cement composition to exhibit excessive set retardation In addition, it has been observed that polycarboxylates, such as described in U.S. Pat. No. 5,369,198, provide good slump but may introduce excessive amounts of air to the resultant structural formation Although a certain degree of intentionally entrained air in the form of microbubbles is desired to enhance freeze-thaw characteristics of the resultant structure, excessive air entrainment is not desired as it can cause reduction in the strength of the structure formed.
Various agents have been proposed to either enhance (air entrainers) or reduce (air detrainers) the air content produced by counteracting the effects other additives have on a particular cement composition. For example, in U.S. Pat. Nos. 5,665,158 and 5,725,657, Darwin et al. disclosed the use of oxyalkylene amine based defoaming agents for formulation with a copolymer of polycarboxylic acid and polyoxyalkylenes of the comb type variety. The general composition claimed was X2N(BO)zR, wherein X represented hydrogen, (BO)zR, or mixtures thereof, R represented hydrogen, a C1-C10 alkyl group, or BNH2, B represented a C2-C10 alkylene group, and z represented an integer from 5 to 200. An alkoxypolyoxyalkylene ammonium polymer was ionically attached to the carboxylate portion of the comb polymer backbone, so as to impart desired air controlling properties to the hydratable cementitious composition being treated.
In U.S. Pat. No. 6,139,623, Darwin et al. disclosed a combination having a superplasticizer comprising a polyacrylate comb polymer emulsified with an antifoaming agent selected from the group consisting of a composition having the formula (PO)(O—R)3 wherein R is a C2-C20 alkyl group, a phosphate ester, an alkyl ester, a borate ester, a silicone derivative, and EO/PO type defoamer; and a surfactant that was operative to stabilize the emulsified comb polymer and antifoaming agent. The surfactant was selected from the group consisting of (1) an esterified fatty acid ester of a carbohydrate selected from the group consisting of a sugar, sorbitan, a monosaccharide, a disaccharide, and a polysaccharide; and (2) a C2-C20 alcohol having EO/PO groups.
Short of being attached directly to the superplasticizer polymer, conventional air detraining agents are not readily made compatible with the polycarboxylic acid type superplasticizers, or are not otherwise stable when added together in an aqueous solution. Separation of the polycarboxylate superplasticizers and defoamers can lead to inconsistent air contents in cementitious mixtures which hinders achievement of the desired result. While attempts have been made to achieve single compositions having the ability to enhance flowability without excessive air entrainment, many of these attempts have not generally produced the desired stability for extended periods.
Thus, it is highly desired to have a single, storage stable cement admixture that imparts a high degree of slump or maintains this degree of slump over an extended period of time when administered to a structural hydratable cement composition, while avoiding excessive set retardation and providing suitable air entrainment properties to the resultant hydraulic cement structure. It is desired to have a cement admixture capable of providing slump, set and air entrainment properties which are consistent over an extended period throughout manufacture, storage, shipping and job site storage, without having the problems of dissociation, separation and the like.
Thus, in view of the foregoing, the inventors believe that a novel water reducing admixtures (or “superplasticizer”) and defoaming agent system are needed for modifying hydratable cementitious compositions.